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My 77 f-150 4x4 with a 400 has a header leak. I'm debating on whether to go back with headers or manifolds. I'm only considering manifolds b/c of drivehshaft clearance.
Any thoughts one way or the other? Power loss? Probably would have to get a new whole exhuast with manifolds b/c they wouldn't fit existing pipes and they are too old to be just adding pipe too.
For me the issue is if it's a daily driver and your committed to keeping it for years then I would put more money into it. If it's a reserve vehicle for chores then Im not so concerned about gas mileage or power. The other issue is how much life is there left in the rest of the exhaust system.
If you fix the header leak then you'll notice a increase in perfomance, and if you go back to manifolds then your power will be about all the same as leaking headers.
I am build a 460 bronco and plan on running the stock manifolds. The motor is stock and I have no need to make it a race truck. All though it will be a fully restored bronco I figure the manifolds will be just fine for me. I've owned 460 4x4's in the past with stock manifolds and headers and liked them both. I know you have a 400 but thought I would share my views on the subject.
Unless you have very high quality headers, they are more of a pain than the 6000 RPM 5% horsepower increase than they are worth. The good, top of the line headers are a completely different story because they normally don't leak and work very well. However, the cheaper, lesser quality headers from my experience seem like they always have a leak somewhere that needs to be fixed. After spending all your weekends fixing leaking headers and not fishing, most people end up changing back to the factory manifolds or buying high quality headers. Also, just a note, headers don't really enhance performance below 3500 RPMs at all in a non race motor. In other words, in your stock motor, your manifolds will work more than fine. If you don't believe me check out comparisons that are often made in hotrod magazine. The difference between headers and manifolds in a stock motor is negligible up until about 5000rpms.